Introduction
Robust hatchery performance increasingly relies on advanced microbial management strategies. Rather than merely limiting the proliferation of harmful microorganisms, modern approaches aim to actively shape beneficial microbial ecosystems that can support animal health, improve rearing conditions and strengthen overall biosecurity. Within this framework, the targeted use of has become a key tool, contributing to a paradigm shift from corrective disease treatments towards proactive, efficiency-oriented microbial management. Live food organisms such as rotifers and Artemia play a critical role in early larval rearing, but they can also act as vectors for opportunistic and potentially pathogenic bacteria. Optimizing microbial control during live food production is therefore essential to reduce microbial risks at the larval stage. In this study, different strategies for the application of were compared in order to modulate the bacterial flora of ready-to-feed rotifers and Artemia, with the objective of improving bio-encapsulation efficiency and overall microbial stability of live food.
Materials and methods
Application in rotifers
Rotifers were cultured on a mixed diet consisting of VitAlgae Nanno, RoBoost and fresh baker's yeast. At the end of the culture period, rotifers were enriched with Easy Dry Selco (EDS) to optimize their nutritional profile prior to feeding. Following enrichment, several microbial management strategies were evaluated. These strategies combined the use of a natural Vibrio controller (Sanocare SURE) with Sanolife MIC-F, which were applied either with or without a prior germination step, and at different concentrations ranging from 2 × 107 to 2 × 108 CFU ml-1. In one treatment, Bacillus spp. were additionally administered on a daily basis directly in the culture tank at a concentration of 2 × 104 Bacilli ml-1. To characterize the microbial community associated with the rotifers, bacterial plate counts were performed on a general culture medium (TSA and on a selective medium for Vibrio spp. (TCBS). The presence and growth of Bacilli were assessed after incubation of TSA plates for 24 h at 37°C. In parallel, rotifer samples were analyzed using Illumina-based 16S rRNA gene sequencing in order to determine the most abundant bacterial phyla.
Application in Artemia
SEP-Art D-FENSE cysts were hatched and harvested after 21h, after which the were transferred to enrichment tanks. In one treatment, added directly to the enrichment water after an appropriate germination step (1 h at 30°C), at a dosage of 1 g of germinated MIC-F per liter of enrichment water. Artemia nauplii were then introduced into this matured water and subsequently enriched with EDS.
In additional treatments, enriched Artemia were first harvested, cleaned and concentrated before the addition of probionts. Different dosages of germinated Bacilli were tested at varying nauplii concentrations, up to a maximum of 8 million nauplii.l-1. The incorporation of into the Artemia was evaluated at different time intervals following administration. As for rotifers, microbial plate counts were carried out and 16S rRNA gene amplicon sequencing was performed to characterize the bacterial communities associated with the Artemia nauplii.
Results
The results indicate that , when combined with the appropriate use of bacteriostatic products during live food preparation, can be effectively bio-encapsulated in both rotifers and Artemia. Across all tested application strategies, a clear modulation of the microbial community was observed. In particular, all treatments led to a reduced presence of Proteobacteria in the live food, accompanied by an increased relative abundance of Firmicutes, including Bacillus spp.
The use of , specifically SURE rotifer D-FENSE Artemia, contributed to a reduction of Vibrio loads in the live food. This reduction appeared to facilitate . Multiple application routes proved successful, highlighting the possibility to adapt microbial management protocols to different operational conditions in hatcheries.
Discussion
This study demonstrates that targeted microbial management strategies are effective tools for modulating the bacterial communities associated with rotifers and Artemia. all evaluated application scenarios, the combined use of the relative abundance of Proteobacteria, including Vibrio spp., while promoting an Firmicutes, particularly Bacillus spp.The use of SURE and D-FENSE not only limited the of opportunistic bacteria but also enhanced uptake and bio-encapsulation efficiency. incorporation of germinated Bacill was achieved through both enrichment-water application and post-harvest treatment of live food, the flexibility and robustness of the proposed . Overall, these results support the integration of with optimized as a proactive approach to control live food microbiota, biosecurity and more stable microbial conditions in marine larviculture, in previous findings on Bacillus-based microbial management.
References
Avella, M.A., Gioacchini, G., Decamp, O., Makridis, P., Bracciatelli, C. & Carnevali, O. (2010). Application of multi-species Bacillus in sea bream larviculture. Aquaculture, 305, 12–19. https://doi.org/10.1016/j.aquaculture.2010.03.029